This invention relates to auxiliary combustor systems for use with combustion engines. More specifically, this invention relates to an improved combustor system particularly for use with turbocharged reciprocating engines, and for providing closely controlled combustor operation at virtually all engine operating conditions.
Auxiliary combustor systems for use with combustion engines are well known in the prior art. Specifically, such combustor systems are provided with combustion engines such as a turbocharged diesel engine wherein the available energy level of engine exhaust gases at relatively low speed conditions is insufficient to drive the turbocharger to provide the desired turbocharger boost to maintain engine load-carrying capacity. Accordingly, an auxiliary combustor is provided for supplementing the energy level of the exhaust gases supplied to the turbocharger at these relatively low speed conditions, and thereby supplementally drive the turbocharger to provide the desired boost pressure.
Prior art combustor systems have required a supply of fresh charge air to the combustor in order to obtain and maintain propagation of a combustor flame. In this regard, it has been common practice to provide bypass means for bypassing a portion of the compressed charge air from the turbocharger around the engine, and to position the combustor in the bypass means. Importantly, the turbocharger has been sized so that excess charge air is always available whereby fresh air is supplied to the combustor at all conditions of engine operation to maintain a combustor flame. See, for example, U.S. Pat. Nos. 3,048,005; 3,570,240; and 3,996,747. However, with these systems inefficient quantities of fuel are burned in the combustor in order to maintain the desired high energy level of gases flowing through the combustor. Moreover, secondary ignition of any fuel remnants in the engine exhaust gases is not possible.
Other prior art combustor systems have attempted to connect a combustor in series, or in-line, with exhaust gases exiting the engine. In this manner, the energy level of the exhaust gases is boosted for supplementally driving the turbocharger, and any remnants of unburned fuel in the exhaust gases are ignited to reduce system smoke and emissions. However, in the prior art, it has been found that the ignition and sustainment of a flame in the in-line combustor is particularly difficult in the substantially vitiated exhaust gas atmosphere. See, for example, U.S. Pat. Nos. 2,620,621; 2,633,698; 3,736,752; 3,849,988; 3,949,555; 3,988,894; 3,996,748; 4,004,414; 4,009,574, and 4,026,115. However, these systems are undesirable in that they, too, require an oversized turbocharger for providing fresh charge air to the combustor at all times to maintain the combustor flame. This continuous addition of charge air to the combustor results in fuel-inefficient combustor operation, but has heretofore been necessitated by the inability of prior art systems to operate without fresh air.
Various attempts have been made to improve the efficiency of operation of prior art auxiliary combustor systems, and thereby at least partially minimize the efficiency penalties inherent in a constant supply of fresh charge air to the auxiliary combustor. One such attempt comprises the inclusion of a heat exchanger for preheating charge air supplied to an auxiliary combustor mounted along a bypass conduit. See for example, U.S. Pat. Nos. 2,620,621 and 2,840,866. Another design attempt includes injector means for injecting exhaust from an auxiliary combustor into the engine exhaust gas stream. However, because these systems still require the constant supply of fresh charge air to the auxiliary combustor, those systems do not provide for optimum fuel efficient operation.
The combustor system of this invention overcomes the problems and disadvantages of the prior art by utilizing apparatus and methods for maintaining controlled fuel-efficient combustion in an in-line combustor without requiring the continuous addition of fresh charge air to the combustor.